1 introduction 2 testing hardware

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Transkript

1 introduction 2 testing hardware

Sborník vědeckých prací Vysoké školy báňské - Technické univerzity Ostrava
číslo 1, rok 2008, ročník LIV, řada strojní
článek č. 1577
Jan BABJAK*, Petr NOVÁK **
MAXON DC MOTOR CONTROL BY MF624 I/O CARD
ŘÍZENÍ DC MAXON MOTORU V/V KARTOU MF624
Abstract
The article describes principles and shows examples of driving small Maxon DC motors using
the multifunction I/O card MF624 from Humusoft. For speed control, one of Pulse-Width Modulation
(PWM) unit installed on this card is used. Analog input and encoder input are used for measuring of
motor speed and motor position. For educational and test purpose a small board connecting all parts
(driving and measure motor, user inputs and outputs) to I/O card was developed and realized. For
card control we use programming tools Visual Basic .NET and the Matlab software. Examples
demonstrating the basic electric motor control and regulation task were developed for both of these
software environments.
Abstrakt
Článek popisuje principy a příklady řízení malého stejnosměrného motoru Maxon za použití
multifunkční vstupně výstupní (V/V) karty MF624 od společnosti Humusoft. Pro řízení rychlosti
motoru je použit jedna z jednotek generující pulzně-šířkovou modulaci (PŠM), které jsou na kartě
přítomny. Pro měření rychlosti je možno použít analogový signál – generovaný druhým motorem ve
funkci tachodynama („měřicí motor“), nebo klasického enkodéru. Pro polohové řízení je dispozici již
zmiňovaný rotační enkodéru. Pro výukové a testovací účely byl navržen a realizován malý modul,
který spojuje všechny komponenty (hnací a měřící motor, uživatelské vstupy a výstupy) s V/V
kartou. Pro ovládání karty používáme programovacího nástroje Visual Basic.NET a software Matlab.
Pro ty to softwarová prostředí byly vytvořeny příklady demonstrující základní úlohy řízení a regulace
elektromotorů.
1 INTRODUCTION
Research on the Department of robotics at VŠB-TU Ostrava is focused on mobile robots. Basic elements of locomotion subsystem of any mobile robots are motors, especially DC electric motors. For correct work of mobile robots we must know how to control the speed and position of these
motors. For driving of DC motors, PWM signals magnified by H-Bridge device are used. Speed of
this motor can be measured by Incremental Rotary enCoder (IRC) or by analog value of induced
voltage. To compare differences between this ways of speed measure principles, we used pair of DC
motors. One of these motors is powered and the other one serves only as a measuring device. To connect all of these signals to PC, we use a multifunction I/O card which offers an easy way to create
programs to motor control and regulation.
2 TESTING HARDWARE
For testing and measuring of DC motor characteristics we must be able to connect all the electronics signals to the control system for further processing. For these reasons we developed a small
unit which allows to connect these signals to the multifunction I/O card for standard PC with PCI
bus. To drive this measuring set, we use one DC motor connected by a clutch to another DC motor
which serves as a measure. This measuring motor is equipped by an encoder whit 64 Counts-Per*
Ing. BABJAK Ján, Department of Robotics, Faculty of Mechanical Engineering, VŠB-Technical University of
Ostrava, 17.listopadu 15, Ostrava-Poruba, tel. (+420) 59 6995757, [email protected]
**
doc. Dr. Ing. NOVÁK Petr, Department of Robotics, Faculty of Mechanical Engineering, VŠB-Technical
University of Ostrava, 17.listopadu 15, Ostrava-Poruba, tel. (+420) 59 6993595, [email protected]
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Revolution (CPR) used to exact position and speed measuring. In principle, every DC motor can by
used as DC Tachometer which can provide analog information of its speed. This property is used to
measure motor speed in another way which allows us to compare results of both of these measurement methods.
Fig. 1 Block layout of the motor control testing device
This configuration of testing hardware allows to realize various motor speed and position control task. The driving motor is powered by 12V power output directly from the I/O card. This is the
reason why we need no external power source. The testing hardware is equipped with a simple user
interface for basic motor control – it provides two digital inputs (red and green button), two digital
outputs (red and green LED) and one analog input (potentiometer)
Fig. 2 Image of the measuring board
3 MEASURED TASKS
The goal of this measuring is to get a comparison between the exact digital value of speed of
the driven motor taken from IRC encoder and induced analog value from the DC tachometer. The
result of this measuring is described on the following graph. The blue line represents the duty factor
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of Pulse-Width Modulation. At the beginning of the measuring, it is set to zero and then it is increasing to 100% and back to zero again. Value from the encoder is shown as a red line and the analog
value as a green line.
9000
8000
7000
6000
5000
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3000
2000
1000
0
0
500
1000
1500
2000
2500
Fig. 3 – Comparison between IRC (red) and DC Tacho analog value (green), duty factor
of PWM is blue (0 – 100%)
From this measuring we can say that the information about speed of a DC motor taken from
IRC is almost equivalent to the information taken from a DC tachometer. The reason of the difference
between the red and green lines shown on the graph is only the different scale of the data.
Another task which can be done with this hardware is measuring of electrical characteristics of
any electric signal on board. For this task we need two-channel oscilloscope to show all the important
signals. Typical signals are shown at the followed images.
Fig. 4 – PWM waveform
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Fig. 5 – IRC waveforms (channel A, channel B)
Fig. 6 – Waveform of a motor power feed
We can see a waveform of PWM signal used to control speed motor (Fig. 4), two waveforms
from channel A and channel B from incremental rotary encoder (Fig. 5) and a waveform directly
from the power feed of the driving motor (Fig. 6). With the digital oscilloscope’s measure function,
we can verify all parameters of these signals. We can check frequency, duty of PWM and other electric parameters.
Another example of use of this testing module is to realize a simple “Device in the Loop” architecture with Matlab Simulink environment and DC motors. Model of a regulator is realizing the PRegulation function. Output of the regulator is connected to the driving DC motor and input of the
regulator is acquired from DC tacho analog value. Matlab Simulink has no direct support for this
multifunction I/O board so we have to use MATLAB function blockset to get direct access to the I/O
ports of this card. On the next figure, we can see a simple DC motor speed regulation loop. The desired value of speed is taken from the analog value from a potentiometer installed on the user interface on this testing board.
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Potentiometer
(Desired value)
Analog input
(Actual Value)
DC motor -> DC Tacho
(Device In the Loop)
Fig. 7 Model of the P-Regulator in Matlab Simulink environment
Using Matlab or Matlab Simuling we can realize any type of regulator to control DC motor
(for example motors on mobile robot). We can verify the behaviour of our regulator in a real case
before we use this particular algorithm to make a program for microprocessor which can control DC
motors without the PC and Matlab.
We can also control this multifunctional I/O card and testing motors from Visual Basic .NET.
A screenshot from the testing application developed at this environment is at fig. 8.
Fig. 8 – Control application written in Visual Basic .NET
With this example application we can control speed of motors. We have the information about
speed of a motor from the analog input (DC Tacho) and encoder. This information is presented on the
analog panel meter. We also have access to the I/O user interface (LEDs and buttons). PI regulation
was implemented in this application, too. We can switch modes of operation by radiobuttons at the
“Speed Control mode” section. The application is designed for testing and educational purposes.
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4 CONCLUSION
With this testing board we can verify any small DC electromotor speed and position controlling algorithm before it will be implemented to an embedded control system (for example to microcontroller). This device is also useful to demonstrate the principles of DC motors control to students
at laboratory lessons.
REFERENCES
[1] NOVÁK, P.: Mobilní roboty – pohony, senzory, řízení. Nakladatelství BEN - technická literatura Praha, 250s, 2005. ISBN: 80-7300-141-1.
[2] NOVÁK, P.: Mikropočítačové řídicí systémy. 1. vyd. Ostrava: VŠB, 2002. ISBN: 80-2480291-8.
[3] BABJAK, J.: Řízení mobilního robotu neuronovou sítí, (Diploma thesis), Ostrava: katedra robototechniky, VŠB-TU Ostrava, 2006, 76 s.
[4] ATMEL: Procesor ATMega8 – Datasheet. Available:
http://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf
[5] MAXON: On-line catalogue A-Max. Available: http://www.maxonmotor.com/A-max.asp
[6] ST MICROELECTRONICS: L298 – Dual Full-Bridge Driver – Datasheet. Available:
http://www.st.com/stonline/products/literature/ds/1773.pdf
[7] manual MatLab-Simulink,
[8] BALÁTĚ, J. Automatické řízení. Praha : Nakladatelství BEN, 2003, 663 s. ISBN 80-7300020-2.
Reviewers:
ing. Roman Dudek, ESP, Insisa, a.s., Ostrava
ing. Marcel Boščík, ABB, Robotics Division, Ostrabva-Hrabová
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